Tubular heating element for furnaces or the like



Patented Apr. 25, 1939 I PATENT OFFICE TUBULAR HEATING ELEMENT FOR FURNACES OR THE LIKE Cary H. Stevenson, Chicago, Ill., assignor to Lindberg Engineering Company, Chicago, Ill., a corporation oi' Illinois Application December 6, 1937, Serial No. 178,266

Claims.

culation of air or gases throughout the interior of the heating chamber, thereby promoting the equal distribution of heat to all points Within the chamber and counteracting any tendency toward stratification within the chamber, which is of particular importance in cases where metallic objects are being subjected to heat treatment of a predetermined character and degree, and especially where gases are employed within the heating chamber to advantageously affect the results of the heat treatment.

Further objects and details will appear from a description of the invention in conjunction with the accompanying drawing, wherein- Figure 1 is a longitudinal sectional elevation of a heat treating furnace embodyingA the features of the present invention;

Fig. 2 is a cross sectional elevation taken on line 2 2 of Fig. 1; and

Fig, 3 is a detail in perspective showing the tubular heating elements ot the present invention.

As shown for purposes of illustration, the invention is applied to a heat treating furnace having outer side walls IU, a base II, and a top I2. The heating chamber is provided with a lining which includes side facings I3, a base Il, and an arched roof I5. The furnace also includes a rear outer wall I6, a rear lining I1, and a door I8 connected with a counterweight I9 for opening and closing the forward aperture 20, which afradiators for the purpose of applying heat beneath the metallic floor 2l.

The heating elements which more particularly form the subject matter of the present invention are located within the heating chamber 25, and as shown are arranged along the side Walls thereof and partially along the ceiling and within the door I8, although a diierent arrangement of these heating elements is within the scope of the present invention, and the particular number and location of the heating elementsy will be determined with due consideration to kthe degree of heat required and the particular purpose for which the furnace is intended. Asv shown, each of the heating elements is of open ended tubular form, and these elements may be of the` straight vertical formation 26 or of the arched over formation 21.

As shown, one of the side walls of the heating chamber is lined with a multiplicity of the r straight heating elements 26, which areformed of a suitable resistance alloy, as for instance 80% nickel and 20% chromium, which when energized will produce temperatures in the heating chamber up to 2100 F., or more for metal treating purposes. It will be understood also that the arched heating elements 21 are of a like composition and similar in ail respects to the vertical heating elements 26 except in matter of configuration, the upper ends being bent over to follow the curvature of the arch, so that a more extended convection currentilow of heated air or gas will result.

The straight vertical heating elements 26 and the arched heating elements 21 are electrically connected in staggered relation soas` to operate in series in the conduction of the electric current, and with this end in view the lower ends of a pair of tubular heating elements are both welded to a lower conductivel bracket plate 28, while the upper ends of the same adjoining tubes are welded to adjacent upper bracket plates 29, which are spaced or otherwise insulated from one f another, with the result that the current iiow will be in a sinuousy path or series relationship throughout the 'entire set of tubular heating elements which constitute the group. The samearrangement obtains on efxch side of the heating chamber, althouji in the case of the arched over heating elements 21, the upper conductive bracket plates are secured to the ceiling of the chamber, rather than to the wall thereof as in the case of the straight heating elements 26.

In addition to the above, a group of straight tubular heating elements 30 is mounted within a recess 3| on the interior face of the. door Il and welded to conductive lower and upper brackets 28 and 29 similar in all respects to those previously described. If desired, additional groups of tubular heating elements similarly supported and in conductive relation to one another can be secured to the rear wall of the heatinsr chamber or the remainder of the ceiling thereof, depending upon the extent to which it is desirable to multiply the number and arrangement of such heating elements within the space contiguous to the interior walls of the heating chamber.

Suitable electrical connections are provided for supplying the necessary current for circulation through the conductive bracket supports and the tubular heating elements, and such connections can be suitably arranged to simultaneously energize all of the heating elements or to energize one or more groups thereof, depending upon the degree of heat required within the interior of the heating chamber; and gases required in maintaining a gaseous atmosphere may be admitted through a tube 32.

In use, the current supphr will be regulated to energize the heating elements in the number and` to the extent required to secure the desired temperature, and as the temperature of the heating elements is elevated they will begin to radiate heat both from the exterior and interior surfaces of the tubes, which quickly tends to establish convection currents through the tubes which act in the capacity of ues to direct the currents of air or gas upwardly from a point near the floor toward the ceiling of the heating chamber, thereby not only promoting dissemination of heat but also preventing stratification, thereby maintaining equality of conditions throughout the heating chamber, so that metallic objects deposited therein for heat treatment will be subjected at all times to a degree and quality of heat which can be predetermined and maintained throughout the heating period. This is of particular importance in cases where the natural air is commingled with certain gases which it may be desirable to employ in the creation of a special atmosphere best calculated to influence the heat treatment, and in which it is necessary to thoroughly and uniformly commingle gases with the air in order to maintain uniform conditions, both as to the degree of heat and the quality of the atmosphere throughout the heating chamber.,

The means employed for mounting the tubular heating elements not only subserve the function of supporting the open ended tubes in position but also act as conductors, so that in the event it becomes necessary to replace any tube or its mounting, the effected parts may be sawed out and removed preliminary to the substitution of new parts, without disturbing the remainder of the system. At the same time thearrangement of the tubes is one which does not in any substantial degree obstruct the interior of the chamber or otherwise complicate the furnace as a whole.

Although the tubular heating elements of the present invention have especial value in a heat treating furnace of the character heretofore described,it is not the intention, unless otherwise indicated in the claims, to limit the use of such elements to a furnace of this particular charac- 4to be heated when electrically energized and in communication at different elevations with the interior of the chamber for disseminating heat thereinto by radiation and convection, and electrically conductive bracket means secured to the structure and to the heating elements for supporting the heating elements in series arrangement at vertically separated points and supplying current thereto, in series through the bracket means and tubes.

2. In combination with a chambered structure, a multiplicity of tubular heating elements mounted along the inner wall of the chambered struc'- ture and having openings communicating at difi'ering elevations with the interior of the chamber to provide for convective heating currents through the tubular heating elements, said elements being adapted to be heated when electrically energized, and upper and lower conductive mountings for supporting and energizing the heating elements. the upper and lower mountings engaging adjacent tubes in staggered relation to provide for a series flow of the current.

3.In combination with a heating furnace, a multiplicity of open ended tubular heating elements arranged in parallel spaced relation along the interior wall of the furnace and having their open ends positioned at differing elevations to induce convective heating currents, and upper and lower bracket means supporting and connecting adjacent tubular heating elements in staggered relation at the upper and lower points of connection to provide for a series current flow of electricity through the heating elements and bracket means.

4. In combination with a heating furnace having side walls and an arched ceiling, a multiplicity of vertically disposed tubular heating elements open at their ends and adapted to be heated when electrically energized, and conductive bracket means for supporting the upper and lower ends of the heating elements adjacent the walls oi' the heating chamber and supplying current thereto, some of the tubular heating elements being extended in arching relation and in close proximity to the ceiling of the furnace.

5. In combination with a heating furnace having side walls and an arched ceiling, a multi- CARY H. STEVENSON. 

